Conventionally, when manufacturing a switching element, a rectangular chip cut out from a circular wafer is mounted on a metal plate or the like. Crystal defects are present in the wafer, and chips with crystal defects cannot be used. When a chip area is large, the probability of including crystal defects in the chip is so high that the yield can deteriorate. On the other hand, when the chip area is small, the probability of including crystal defects in the chip is so low that the yield can be improved. Reducing the chip area improves the yield, thereby achieving the cost reduction of the switching element.
Compared to the switching element having the large chip area, the switching element of the small chip area has the small current capacity. However, it is possible to achieve an increase in current by connecting the switching elements of the small chip areas in parallel. Patent Literature 1 discloses a technique in which when switching elements are connected in parallel, the inductances of individual signal lines which supply driving signals to the parallel-connected switching elements are made equal to one another in order to prevent the switching element from malfunctioning or being damaged due to the difference in the switching timing among the switching elements.
Patent Literature
Patent Literature 1: Japanese Patent No. 5559265
Unfortunately the above-described conventional technique poses the problem of equalization of the inductances being difficult due to the relationship with positions of terminals used for connection to the outside of the module, or a low degree of freedom of wire routing in the module when a plurality of switching elements is mounted in the same module. To equalize the inductances, it is necessary to adjust switching elements in conformance to switching elements provided with the longest signal lines, even if the adjusted switching elements could have otherwise shorten their signal lines. A problem with this case is that the switching time is prolonged and the switching loss increases. To switch the switching elements at high frequencies, it is necessary to prolong the dead time provided to avoid the simultaneous short-circuiting of the switching elements of the upper and lower arms, which results in the problem of the potential voltage distortion or the increase in iron loss of the motor due to the voltage distortion.